Field observations of C2 and C3 organosulfates and insights into their formation mechanisms at a suburban site in Hong Kong

Yuchen Wang; Shumin Liang; Michael Le Breton; Qiong Qiong Wang; Qianyun Liu; Chin Hung Ho; Bin Yu Kuang; Cheng Wu; Mattias Hallquist; Rongbiao Tong; Jian Zhen Yu

doi:10.1016/j.scitotenv.2023.166851

Field observations of C₂ and C₃ organosulfates and insights into their formation mechanisms at a suburban site in Hong Kong

Sci Total Environ. 2023 Dec 15:904:166851. doi: 10.1016/j.scitotenv.2023.166851. Epub 2023 Sep 8.

Authors

Affiliations

¹ College of Environmental Science and Engineering, Hunan University, Hunan, China; Division of Environment and Sustainability, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China.
² Department of Chemistry, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China.
³ Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden.
⁴ Division of Environment and Sustainability, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China.
⁵ Division of Environment and Sustainability, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China; Institute of Mass Spectrometer and Atmospheric Environment, Jinan University, Guangzhou, China.
⁶ Division of Environment and Sustainability, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China; Department of Chemistry, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong, China. Electronic address: jian.yu@ust.hk.

PMID: 37673264
DOI: 10.1016/j.scitotenv.2023.166851

Abstract

Organosulfates (OSs) are formed from volatile organic compounds (VOCs) and their oxidation products in the presence of sulfate particles. While OSs represent an important component in secondary organic aerosol, the knowledge of their formation driving force, mechanisms, and environmental impact remain inadequately understood. In this study, we report ambient observations of C_2-3 oxygenated VOCs derived OSs (C_2-3 OSs) at a suburban location of Hong Kong during autumn 2016. The C_2-3 OSs, including glycolaldehyde sulfate (GS), hydroxyacetone sulfate (HAS), glycolic acid sulfate (GAS), and lactic acid sulfate (LAS), were quantified/semi-quantified using offline liquid chromatography-mass spectrometry analysis of aerosol filter samples. The average sum concentration of C_2-3 OSs was 36 ng/m³. Correlation analysis revealed that sulfate, surface area, and liquid water content were important factors influencing C_2-3 OS formation. Online measurement with an iodide High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer (HR-ToF-CIMS) coupled with the Filter Inlet for Gases and AEROsols (FIGAERO) was also conducted to monitor C_2-3 OSs, and their potential oxygenated VOC precursors in both gas- and particle-phase, and aerosol acidity tracer simultaneously. Our measurements support that glycolaldehyde/glyoxal, hydroxyacetone, glycolic acid/glyoxal, and lactic acid/methylglyoxal are likely precursors for GS, HAS, GAS, and LAS, respectively. Additionally, we found strong correlation between C_2-3 OSs and H₃S₂O₈^-, a marker for aerosol acidity, providing field observational evidence for acid-catalyzed formation of small OSs. Based on both online and offline measurements, acid-catalyzed formation mechanisms in particle/aqueous phase are proposed. Specifically, the unique structure of adjacent carbonyl and hydroxyl groups in the C_2-3 oxygenated VOC precursors can facilitate the formation of (1) a five-member ring intermediate via intramolecular hydrogen bond to react with sulfur trioxide through heterogenous reaction or (2) cyclic sulfate intermediate via particle-phase reaction with sulfuric acid to generate C_2-3 OSs. These proposed mechanisms provide an alternative pathway for the liquid-phase production of C_2-3 OSs.

Keywords: Aerosol acidity; Glycolic acid sulfate; Hydroxyl organosulfates; Organosulfates; SOA formation mechanism; Secondary organic aerosol.